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CMP Beaver conversion - 12/16/2012 11:41 PM   
tomd-RCU


 

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Status: offline 		The Beaver was ordered from HobbyKing. I received it in top condition. Everything was well packaged and I was surprised at the quality of the plane. It is a balsa built and covered with shrink plastic.

I am thinking of using an OS 32SX engine with a Pitt's style muffler.

The work involves removing the already built electric engine mount and replace it with a suitable mount for glow.

Of course a pushrod and an extra servo will have to be added for the engine as also a fuel tank.





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RE: CMP Beaver conversion - 12/16/2012 11:52 PM   
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Status: offline 		The front of the firewall needs to be flush with the front of the fuselage. Since I will be using 1/4 inch plywood to build it, I cut the original firewall 1/4 of an inch inside the front of the fuselage.

To keep the new firewall in place, I glued inside the remaining firewall four pieces of 1/8 inch plywood. Tabs were cut on these pieces to hold the firewall in place.
Triangle stock was used to reinforce the whole structure.

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RE: CMP Beaver conversion - 12/17/2012 12:11 AM   
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Status: offline 		This is a picture of the original electric motor mount.

You can clearly see where I made the cuts.

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RE: CMP Beaver conversion - 12/17/2012 2:34 PM   
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Status: offline 		Considering you only using a .32, do you really need to use 1/4" ply for the new firewall? Save some weight and use 1/8".

just a thought.

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RE: CMP Beaver conversion - 12/18/2012 12:14 AM   
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Status: offline 		Here is a picture of the firewall installed.

I made sure I gave it about 3 degrres of downthrust and close to two degrees of right thrust.

Twin Flyer, yes 1/4 inch plywood might be overkill bit it is my first conversion. Is there a rule of thumb when choosing plywood thickness vs engine displacement ?

My calculations tell me I might need some extra weight in the front because of the short nose moment of this plane. If this turns out to be the case then the extra weight of the plywood will pay off.

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RE: CMP Beaver conversion - 12/18/2012 12:18 AM   
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Status: offline 		The open space was closed off using 1/16 plywood.

I used high temperature gasket material to seal the joint betwwen the firewall and the rest of the enclosure.

Because this enclosure covers the cowling supports, I made sure I drilled holes in the enclosure to access the T-nuts installed by the manufacturer.

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RE: CMP Beaver conversion - 12/19/2012 2:31 AM   
ckreef


 

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Status: offline 		Judgeing from past experience 3 degrees  of down and 2 degrees of right sounds like way too much. Every conversion I have  done to date needs some thrust taken out compared to what the electric setup had built in (and I use engines on the larger size for the plane). I would rather start either flush or with 1 and 1 and add washers as needed.


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RE: CMP Beaver conversion - 12/20/2012 11:11 AM   
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Status: offline 		ckreef,

Thank you for your input.


What you say does make sense. When the throttle is activated, an electric motor develops it's torque more rapidly than a glow motor.
I will need to try the airplane and, if need be, I will reduce the thrust incidence.

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RE: CMP Beaver conversion - 12/21/2012 1:27 AM   
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Status: offline 		This picture showas the engine support in place. The engine will be an OS 32SX and it will installed rotated 90 degrees to the right.

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RE: CMP Beaver conversion - 12/21/2012 1:29 AM   
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Status: offline 		This picture shows the engine installed with it's Pitts style muffler.

The throttle arm had to be extended to clear the muffler.

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RE: CMP Beaver conversion - 1/30/2013 6:53 AM   
Kmot



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Status: offline 		You're doing an awesome job!

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RE: CMP Beaver conversion - 1/31/2013 12:17 AM   
tomd-RCU


 

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Status: offline 		Thank you Kmot.

Since glow fuel is used, I need to install a support for the fuel tank at the right height.
This picture shows my work.

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RE: CMP Beaver conversion - 1/31/2013 12:22 AM   
tomd-RCU


 

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Status: offline 		This picture shows the servos installed.

Notice I had to add a third servo for the throttle.

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RE: CMP Beaver conversion - 2/1/2013 8:29 AM   
TKO



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Status: offline 		Hello Tomd,

nice conversion. I bought the Beaver from CMP(The Military version) and for a week ago i did start the conversion to glow and used your "knowledge" for the firewall.
This is almost ready and i'm thinking now about the engine. First i thought the .60 4 stroke is the egine i like for the sound, but a 4 stroke is somewhere an attack on the fuselage of the aircraft and a 2 stroke is not so nice for his sound.
What do you think?
Rgds
Theo(From the Netherlands)



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RE: CMP Beaver conversion - 2/3/2013 1:39 PM   
tomd-RCU


 

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Status: offline 		Hello TKO,

I naturally prefer the sound of a 4 cycle to that of a 2 cycle especially on this type of airplane.

I recently checked the balance of the airplane and with my 32 SX the airplane is a little rear heavy. This tells me that the use of a heavier engine would not need additional front weight. However, I would think that a 60 would be too heavy up front. I think a 46 size engine would be best.

As for 2 or 4 cycles, here is my thinking. Around the circunference of the cowling are three tabs whose holes have to align on T-nuts on the firewall.
If you use a 4 cycle there is a good possibility that 2 of these tabs (the holes) will be blocked by the head of the engine. You will then need to add tabs at different places on the rear circumference of the cowling to keep it in place. Believe me, adding two tabs is not an easy matter. I had to do it for the 32 SX, I imagine it would be more difficult with a bigger engine. Check my picture below and you can see the two extra tabs I had to add. Of course, forget about the fake radial when you add these extra tabs. There is no way you can align the tabs with the T-nuts with the fake radial in place.

Another consideration... a bigger engine means bigger servos. There is no problem in the fuselage. However, It is a diffrent story for the wings. I upgraded my servos to Spektrum's A5030 (these are minis)and I am having a hard time fitting them in the wings. I am almost there.

You are right a 60 size engine would be too much for the firewall. A 40 size 2 cycle would be a better choice even if the sound that we want to hear is not there.
Good luck and post pictures of your work.

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RE: CMP Beaver conversion - 2/10/2013 10:45 AM   
TKO



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Status: offline 		Thanks Tomd for all the information. I have to wait for the delivery of some items from Hong Kong and than i hope to finish this Beaver.
As soon as i start to build the engine on the fuselage i make some pictures.
Last year i was a couple of weeks in Canada to make a roundtrip and visit family of my wife in Edmonton. We started in Calgary and via Jasper, Edmonton to Vancouver Islands and than back to Vancouver for our flight back to the Netherlands. What a beautiful country is Canada
Rgds
Theo



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